1. Field of the Invention
This invention relates in general to engines and in particular to intermittent combustion engines in which the combustion products are used as the thrust producing medium.
2. Description of Related Art
A pulse combustion engine such as a pulse detonation engine is an apparatus which produces a high pressure exhaust from a series of repetitive combustions within a combustion chamber. A fuel is detonated within a chamber, causing a wave which propagates at high speeds. The speeds could approach or exceed Chapman Jouguet detonation velocities. The wave compresses the fluid within the chamber, increasing its pressure, density, and temperature. As the wave passes out the open rearward end, thrust is created. The cycle is then repeated.
The pulse combustion engine (detonation or deflagration or combination of both) contains no means at present to generate shaft power to run electrical and hydraulic systems of the vehicle being propelled. If the pulse combustion engine is combined in an integral manner with a jet engine, then both systems benefit from this combined cycle, in terms of shaft power output and increased Mach number capability. Current production gas turbine engines are limited to an upper Mach number of approximately 2. The strength of the pulse combustion engine is the lack of turbomachinery downstream of the combustion region, which limits the upper useful speed of the jet engine. Combining the jet engine and the pulse engine produces a composite combined cycle engine that can provide shaft power and supply the required thrust over a wide range of speeds. At high speeds (e.g., Mach 4) the jet engine essentially runs at idle, supplying shaft power, but very little thrust. At these same speeds the pulse engine has adequate ram air pressure to supply the required thrust and does not rely on the jet engine for high pressure input air. At lower speeds (e.g., Mach 0 to 1) the jet engine supplies high pressure air to the pulse combustion engines by fan bypass air, compressor bleed or by a shaft which turns one or more independent fans to pressurize the flow going into the pulse jets. For this Mach regime the pulse engine acts as an afterburner for the jet engine or as an afterburner supplement if the jet has an integrated afterburner. This combination of pulse combustion and gas turbine engines can generate high levels of thrust efficiently across a wide range of flight speedsxe2x80x94higher than is possible with either engine separately.
The combined cycle pulse combustion/gas turbine engine of the present invention solves the problems individually associated with each of these engines. The invention includes a gas turbine engine and a plurality of pulse combustion engines that work together over various aircraft speed ranges.
In the first embodiment, the turbine engine includes a housing, a high bypass ratio fan, and a central engine core. The housing has an annular diffuser section outside of the central engine core for diverting bypass air from the bypass fan around the central engine core and out of the housing. The bypass fan typically bypasses one to five parts of air for every one part of air that is ingested by the central engine core.
The pulse combustion engines each include an inlet port, a combustion chamber, and a valve for admitting fuel and air to the chamber. The pulse combustion engines are disposed within the annular diffuser section of the gas turbine engine. As air bypasses the central engine core, a portion of the air enters the pulse engines. Typically, the amount of air allowed to enter the pulse engines by the bypass valve is dependent on the opening and closing rate of the pulse engines"" rotary valves.
In a second embodiment, a similar gas turbine engine having a diffuser section is used. A pulse combustion engine is fluidly connected to the diffuser section by a duct. As air bypasses the central engine core, a portion of the air is allowed to enter the pulse combustion engine through the duct. The duct may or may not include a bypass valve for regulating the amount of air allowed to enter the duct.
Finally, a third embodiment of the present invention includes a series of pulse combustion engines used in conjunction with a jet engine. The jet engine drives a drive shaft connected to an external fan. The fan supplies air to the pulse engines. A clutch is disposed between the jet engine and the fan, the clutch selectively disengaging the fan during certain operational conditions.